Fix #129: use transaction ID from connection's own transaction.
Fix #131:  return datetime w/ UTC zone.
Fix #132:  enforce 64-bit ranges on long values for protobuf attrs.
Fix #133:  preserve PB namespace in Key.from_protobuf.
Add docstrings for API method of g.datastore.key.Key.
Fix #134:  enforce contract that *args must be pairs.
Propose a contract for Key.parent.
Fix #135:  enforce contract for Key.parent().
Incorporate feedback from @dhermes.
Merge branch 'add_key_docstrings' into 133-key.from_protobuf-preserve-namespace
Merge branch 'add_key_docstrings' into 134-key-from_path-contract
Merge branch 'add_key_docstrings' into 135-key-parent-contract
Incorporate feedback from @dhermes.
Incorporate feedback from @dhermes.
Merge branch 'add_key_docstrings' into 135-key-parent-contract
Incorporate feedback from @dhermes.
Don't pass transaction ID to connection.rollback_transaction().

Feedback from @dhermes.
Merge pull request #182 from tseaver/132-enforce_int64_bounds_for_protobuf_values

Fix #132:  enforce 64-bit ranges on long values for protobuf attrs.
Removing keyword "type" from storage.acl.
Using more descriptive entity_type instead of type_.